The supply of mains electricity in modern systems is provided by a complex interplay of generators, distribution and transmission. On the demand side, a similarly complex mix of customers requires variable levels of supply, in an uncoordinated manner. This all occurs in real time. Whilst generators will be contracted to supply certain levels of production for certain time periods during the day, and this is supplemented by supplies being brought on and off line with time scales of tens of minutes, the variability of demand means that the supplies and loads never exactly match. This results in generators increasing speed (frequency) when load is lower than generation and decreasing speed (frequency) when load exceeds generation output.
Regulation service corrects for short term changes in electricity demand, by assisting in matching generation output to demand, and in maintaining the desired frequency. These services may be up regulation, to provide extra power when demand exceeds capacity, or down regulation, when the generated capacity exceeds demand.
One way to provide regulation service is to vary the output of a fossil fuel generator around a set point, particularly gas fired turbines, due to their faster response compared to coal-fired plant. Another source of regulation service is pumped hydroelectric, in which generation output is varied about a base, set point, value. Other systems are known including compressed air and flywheels.
Another way to provide regulation services uses large storage batteries. During times of excess electricity supply, the batteries are charged. When additional output is required for regulation, a power converter is used to produce AC from the DC storage output. This can be done relatively quickly and with high reliability. Although efficient systems to accomplish this exist, there is still a relatively large capital cost associated with the battery system, control electronics, and power electronics for battery based systems.
It is an object of the present invention to provide regulation services in a more efficient way.